We examined brain and cognitive reserve related to bilingualism in older adults with, or at-risk for, Alzheimer's disease (AD) from the Canadian Consortium on Neurodegeneration in Aging and the Quebec Consortium for the Early Identification of Alzheimer's Disease. We used surface-based morphometry methods to measure cortical thickness and volume of language-related and AD-related brain regions. We did not observe evidence of brain reserve in language-related regions. However, reduced hippocampal volume was observed for monolingual, but not bilingual, older adults with AD. Thus, bilingualism is hypothesized to contribute to reserve in the form of brain maintenance in the context of AD.

Evidence from various empirical study types have converged to show bilingualism's potential for serving as a cognitive and brain reserves contributor. In this article, I contextualize, frame the need for and offer some expanding questions in this endeavor, inclusive of empirical pathways to address them. While the set of variables and questions discussed herein are definitively incomplete, they embody a good starting point for shaping future directions in research that considers the role bilingual language engagement can have for the developing mind and brain, inclusive of how various, non-linear factors impact the descent bilinguals of various types take down the proverbial mountain of life.

Accurate measurement of cognitive function is critical for understanding the disease course of Alzheimer's disease (AD). Detecting cognitive change over time can be confounded by level of premorbid intellectual function or cognitive reserve and lead to under- or over-diagnosis of cognitive impairment and AD. Statistical models of cognitive performance that include cognitive reserve can improve sensitivity to change and clinical efficacy. We used confirmatory factor analysis to test a four-factor model composed of memory/language, processing speed/executive function, attention, and cognitive reserve factors in a group of cognitively healthy older adults and a group of participants along the spectrum of amnestic mild cognitive impairment to AD (aMCI-AD). The model showed excellent fit for the control group (χ2 = 100; df = 78; CFI = .962; RMSEA = .049) and adequate fit for the aMCI-AD group (χ2 = 1750; df = 78; CFI = .932; RMSEA = .085). Although strict invariance criteria were not met, invariance testing to determine if factor structures are similar across groups yielded acceptable absolute model fits and provide evidence in support of configural, metric, and scalar invariance. These results provide further support for the construct validity of cognitive reserve in healthy and memory impaired older adults. (JINS, 2012, 18, 1–10)

Cognitive reserve, broadly conceived, encompasses aspects of brain structure and function that optimize individual performance in the presence of injury or pathology. Reserve is defined as a feature of brain structure and/or function that modifies the relationship between injury or pathology and performance on neuropsychological tasks or clinical outcomes. Reserve is challenging to study for two reasons. The first is: reserve is a hypothetical construct, and direct measures of reserve are not available. Proxy variables and latent variable models are used to attempt to operationalize reserve. The second is: in vivo measures of neuronal pathology are not widely available. It is challenging to develop and test models involving a risk factor (injury or pathology), a moderator (reserve) and an outcome (performance or clinical status) when neither the risk factor nor the moderator are measured directly. We discuss approaches for quantifying reserve with latent variable models, with emphasis on their application in the analysis of data from observational studies. Increasingly latent variable models are used to generate composites of cognitive reserve based on multiple proxies. We review the theoretical and ontological status of latent variable modeling approaches to cognitive reserve, and suggest research strategies for advancing the field. (JINS, 2011, 17, 593–601)